1. Field of the Invention
The present invention relates to a method and an apparatus of butt welding and, more particularly, to a method and an apparatus of butt welding which enable to suppress deformation of sheared first and second blanks and enable to butt weld the sheared first and second blanks even in a case where straightness of joint surfaces of the sheared first and second blanks are likely impaired due to the residual stress after the first and second blanks are sheared.
2. Description of Earlier Technology
In earlier technology, at a stage of a producing operation of a side panel outer which is a piece of automobile parts, a tailored blank material is previously produced by jointing a plurality of blank materials by butt welding each joint surface of the plurality of blank materials in a butt welding machine or in a laser welding machine. Generally, there are variable case, for example, a case where each of the plurality of blank materials has same thickness and material quality or another case where each of the plurality of blanks material has different in both the thickness and the material quality. Sequentially, the tailored blank material is worked by pressing operation or stamping operation in a power press machine with desired molds or desired dies, and is made into the side panel outer of the automobile.
Since a residual stress exists in a coiled steel plate, when shearing the blank material by a metal mold of a press machine, it sometimes happens that the residual stress is released with the result that the straightness of the joint surfaces of the blank material is impaired. In this case, it is arranged that in a construction wherein as illustrated in FIG. 1 a relatively large notch or recessed portion is formed in the central part of each of blank materials 503, 511 and joint surfaces 503A, 503B, or 511A, 511B are formed on both sides of each blank material the joint surface has been formed on a forward end portion of the portion that has been sheared in three directions. Therefore, the straightness of the joint surface is largely deteriorated and this raises the problem that even when butting the joint surfaces 503A, 503B of the first blank and the joint surfaces 511A, 511B of the second blank material to each other, a relatively large gap is formed between these butted surfaces and, when butt welding is performed, humping beads are likely to be produced.
The present invention has been made in view of the above-described matters.
It therefore is an object of the present invention to provide a method and an apparatus of butt welding which enable to suppress deformation of sheared first and second blank materials and enable to butt weld the sheared first and second blank materials even in a case where straightness of joint surfaces of the sheared first and second blank materials are likely impaired due to the residual stress after the first and second blank materials are sheared.
To achieve the object, a method of butt welding according to an aspect of the present invention comprises the following steps: pressing first and second blank materials onto first and second loading bases respectively, by clamping devices thereby fixing them; shearing end surfaces of the first and second blank materials thereby forming joint surfaces; and performing butt welding on each of the joint surfaces of the first and second blank materials while these blank materials are maintained in fixed state where the first and second blank materials are pressed by the clamping devices.
According to the present invention, even when after having sheared the end surfaces of the first and second blank materials the residual stress is released and as a result a deformation tends to occur to impair the straightness of the joint surfaces, since the first and second blank materials are held in a state where they are pressed and fixed on the first and second loading bases by the clamping device, it results that the tendency that the straightness of the joint surfaces will be deteriorated is suppressed and the straightness thereof is maintained as is.
And, since in a state where the first and second blank materials are maintained to be pressed and fixed the joint surfaces are butted together, the butting of the joint surfaces are performed with a high precision. Thereafter, butt welding is performed thereon, with the result that highly precise butt welding is realized.
An apparatus of butt welding according to another aspect of the present invention comprises: a first loading base that has a clamping device to clamp a first blank material, the clamping device being capable of holding the first blank material in a state where this blank material is pressed and fixed on the first loading base; a second loading base that has a clamping device to clamp a second blank material, the clamping device being capable of holding the second blank material in a state where this blank material is pressed and fixed on the second loading base; a first shearing machine to shear an end surface of the first blank material pressed and fixed onto the first loading base and thereby forming a joint surface; a second shearing machine to shear an end surface of the second blank material pressed and fixed onto the second loading base and thereby forming a joint surface; and a butt welding machine to perform butt welding on the joint surfaces of the first and second blank materials which are butted each other by the first and second loading base in a state where the first and second blank materials blank materials are maintained to be pressed and fixed onto the first and second loading base, respectively.
According to this aspect of the invention, the deformation that occurs due to the residual stress after having sheared the first and second blank materials by the shearing machine is suppressed by the blank materials being pressed and fixed by the clamping device.
Accordingly, it is possible to perform butt welding on the joint surfaces of the first and second blank materials highly precisely and therefore to realize excellent butt welding.
In the apparatus of butt welding described above, in case where the first and second loading bases are equipped with each of a blank positioning device capable of positioning end portions of the blank materials on the loading bases, each of the end portions of the blank materials has protruded from each of the end edges of the loading bases.
Accordingly, when shearing the end portion of the blank material and thereby forming a joint surface, the portion in the vicinity of the shearing portion of the blank material can be pressed and fixed by a blank holder equipped to the shearing machine and as a result highly precise shearing can be performed.
Furthermore, in case where position pressing and fixing the first and second blanks by the clamping device is set at a location near the shearing surface in order to prevent wrinkle from occurring due to the influence of a plastic deformation at the time of shearing performed by the shearing machine, the wrinkle will be reduced at the position in the vicinity of the sheared portion, therefore the straightness precision at the time of shearing can be maintained.